Identifying the FTL Mapping Schemes of USB Flash Drives

Abstract

NAND flash storage devices, such as USB flash drives and SSDs, have different characteristics from NAND flash chips. They have embedded FTLs that emulate the devices as traditional HDDs. Although they support same interface as HDDs, they show different features from HDDs, especially in the write performance. Even among the flash drives, moreover, shows much differences in performance according to their embedded controllers, whose FTL algorithms are not opened. System softwares cannot manage flash drives efficiently since they do not know inner actions of the devices. In this paper, we propose a simple methodology that estimates the mapping schemes of flash drives. Our method is based on a simple software that requests I/O in pre-defined patterns and analyzes each latency. We tested the method with real USB flash drives and successfully estimated their mapping schemes.